The most commonly used processes for purifying target proteins such as, e.g., monoclonal antibodies, typically employ an engineered cell line (e.g., a mammalian or a non-mammalian cell line) capable of expressing the target protein. Such a target protein may either be secreted into the cell culture media or it may be expressed intracellularly and recovered following lysis of cells expressing the protein.
The target protein typically needs to be subjected to a series of purification steps to separate the target protein from various impurities, e.g., cells, cell debris, DNA, host cell proteins etc.
A typical purification process usually entails subjecting the cell culture feed or media (in case of a secretory target protein) or cell lysate (in case of an intracellular target protein) to a variety of steps, including one or more chromatography steps to isolate or purify the target protein. For example, in case of a secretory target protein, e.g., a monoclonal antibody, the cell culture media is typically subjected to a clarification step followed by a capture step followed by one or more of a cation exchange bind/elute chromatography step and an anion exchange chromatography step.
CHO cells are commonly used for the production of monoclonal antibodies. A typical CHO cell culture feed contains 103 to 109 viruses or virus-like particles and the removal of such viruses or virus-like particles is especially important during the purification process, as many of the target proteins are therapeutic proteins which are directly administered to patients. Generally, virus removal is evaluated based on the amount of total virus removal achieved by the entire purification process, which is desirable to be equal to or exceeding 18 logs, especially in cases where regulatory approval is required.
Generally, each step of a typical purification process is shown to remove some amount of viruses, however, the amount is usually less than 18 logs; and therefore, additional purification steps must be included in the process for adequate virus removal. It is important to establish whether or not a particular purification step can remove a certain amount of virus in order to ensure that adequate virus removal is achieved by the various purification steps in a purification process.
Guidance for virus safety evaluation of samples, e.g., biotechnology products, can be found in “Harmonized Tripartate Guideline: Q5A Viral Safety of Biotechnology Products Derived From Cell Lines of Human or Animal Origin. Fed. Reg. 63(185) 24 Sep. 1998,” prepared under the auspices of the International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH).
Activated carbon has previously been used in water purification applications to remove viruses as well has been incorporated in filtration units for non-specific removal of substances, which may include viruses, from biological fluids, e.g., blood (e.g., see, U.S. Pat. No. 8,123,940)
Further, U.S. patent application Ser. No. 13/565,463, filing date Aug. 2, 2012, incorporated by reference herein in its entirety, describes the use of activated carbon in combination with other media for removal of proteinaceous impurities (e.g., host cell proteins) and DNA from a sample containing a biomolecule of interest (e.g., an antibody).
Lastly, U.S. Provisional Patent Application Ser. No. 61/769,269, filing date Feb. 26, 2013, incorporated by reference herein, describes the use of activated carbon for the selective removal of a protein from a mixture of proteins by changing solution conditions.